International Business Machines Corporation

Peter J Elliott

Anthony R Hearn

Anthony W Leonard

Alan J Betts

David T James

A disk file includes multiple disk surfaces, on which servo information is recorded, with an offset in azimuth from one disk surface to another. Each head comprises a magnetoresistive stripe for reading and an inductive write coil. The servo system reads servo information from each disk in turn, multiplexing the signals from each disk together to form a single position error signal (PES). The separation of the servo multiplexer, attached to the MR stripes, from the write multiplexer, attached to the inductive coils, avoids problems due to contamination of the servo signal by the write signal. A least squares fit is used to generate the PES from the series of servo samples from each disk surface.

Disk file with multiplexed servo system

A magnetic disk drive is provided with a system and method for writing a servo pattern after the head disk assembly (HDA) is sealed. A clock track is written inside the sealed HDA using a Monte Carlo technique. The clock track is read by a magneto-optical head through a window in the HDA housing, and the time transitions therefrom are used to control the product heads. The entire servo pattern for the disk drive is thus written with the HDA unit completely sealed.

System and method for servowriting a magnetic disk drive

A head positioning system with automatic gain control for use in disk information storage apparatus employs multiphase radial position error signals derived from position reference information on the disk to control the position of a transducing head by means of a head positioning actuator. A variable gain amplifier amplifies the signals from the transducing head prior to their application to a position error signal generating means. The gain of the amplifier is controlled in a gain control loop by a gain function. The gain function is derived by combining the differnet phase position error signals to provide, at any position of the head, a measurement of the rate of change of the position error signals per track of displacement. This system affords gain control which is substantially independent of head width and limits variations in offtrack gain between heads.

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Alresford, United Kingdom

Peter J Elliott